Impaired activity of the bile canalicular organic anion transporter (Mrp2/cmoat) is not the main cause of ethinylestradiol-induced cholestasis in the rat.
To test the hypothesis that impaired activity of the bile canalicular organic anion transporting system mrp2 (cmoat) is a key event in the etiology of 17alpha-ethinylestradiol (EE)-induced intrahepatic cholestasis in rats, EE (5 mg/kg subcutaneously daily) was administered to male normal Wistar (NW) and mrp2-deficient Groningen Yellow/Transport-deficient Wistar (GY/TR-) rats. Elevated plasma bilirubin levels in GY/TR- rats increased upon EE-treatment from 65 +/- 8.4 micromol/L to 183 +/- 22.7 micromol/L within 3 days, whereas bilirubin levels remained unaffected in NW rats. Biliary bilirubin secretion was 1.5-fold increased in NW rats but remained unaltered in GY/TR- rats. Plasma bile salt concentrations remained unchanged in both strains, although hepatic levels of the sinusoidal Na+-taurocholate cotransporting protein (ntcp) were markedly reduced. Biliary secretion of endogenous bile salt was not affected in either strain. A clear reduction of mrp2 levels in liver plasma membranes of NW rats was found after 3 days of treatment. The bile salt-independent fraction of bile flow (BSIF) was reduced from 2.6 to 2.0 microL/min/100 g body weight in NW rats with a concomitant 62% reduction of biliary glutathione secretion. The absence of mrp2 and biliary glutathione in GY/TR- rats did not prevent induction of EE-cholestasis; a similar absolute reduction of BSIF, i.e., from 1.1 to 0.6 microL/min/100 g bodyweight, was found in these animals. EE treatment caused a reduction of the maximal biliary secretory rate (S(RM)) of the mrp2 substrate, dibromosulphthalein (DBSP), from 1,040 to 695 nmol/min/100 g body weight (-38%) in NW rats and from 615 to 327 nmol/min/100 g body weight (-46%) in GY/TR- rats. These results demonstrate that inhibition of mrp2 activity and/or biliary glutathione secretion is not the main cause of EE-induced cholestasis in rats. The data indicate that alternative pathways exist for the biliary secretion of bilirubin and related organic anions that are also affected by EE.
Koopen
N R
NR
Groningen Institute for Drug Studies, Laboratory of Nutrition and Metabolism, University Hospital Groningen, The Netherlands.
Wolters
H
H
Havinga
R
R
Vonk
R J
RJ
Jansen
P L
PL
Müller
M
M
Kuipers
F
F
D000818:Animals; D027321:Anion Transport Proteins; D001646:Bile / Q000737:chemistry / Q000378:metabolism; D001647:Bile Acids and Salts / Q000032:analysis; D001663:Bilirubin / Q000097:blood; D015153:Blotting, Western; D001835:Body Weight / Q000187:drug effects; D002352:Carrier Proteins / Q000032:analysis / Q000502:physiology*; D002462:Cell Membrane / Q000737:chemistry; D002779:Cholestasis / Q000209:etiology* / Q000473:pathology; D045166:Estradiol Congeners / Q000494:pharmacology*; D004997:Ethinyl Estradiol / Q000032:analysis / Q000494:pharmacology*; D008055:Lipids / Q000032:analysis; D008099:Liver / Q000737:chemistry / Q000187:drug effects; D008297:Male; D026901:Membrane Transport Proteins; D009929:Organ Size / Q000187:drug effects; D029363:Organic Anion Transporters, Sodium-Dependent; D051381:Rats; D011922:Rats, Mutant Strains; D017208:Rats, Wistar; D027981:Symporters; D013997:Time Factors
D027321:Anion Transport Proteins; D001647:Bile Acids and Salts; D002352:Carrier Proteins; D045166:Estradiol Congeners; D008055:Lipids; D026901:Membrane Transport Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; C071908:sodium-bile acid cotransporter; D004997:Ethinyl Estradiol; D001663:Bilirubin